Head-and-neck tumor is a tumor formed in the ear, nose, pharynx, larynx, cervix, facial surface, oral cavity, or the like; particularly, a malignant one is prevalent in men 50 years old or more and accounts for 6% of all malignant tumors. The incidence rate thereof increases with increasing age; 650,000 people are annually affected thereby in the whole world and of these, 350,000 die of the malignant tumor (see Non-Patent Document 1). Among others, laryngeal cancer is the most common disease in the head and neck area; the number of fatalities is estimated to increase according to the future prediction of the annual death number due to the laryngeal cancer by the Cancer Statistics White Paper.
The diagnosis of head-and-neck tumor is performed by staging using endoscopy and various imaging tests (CT, MRI, PET, ultrasonography, etc.) and tissue diagnosis by biopsy, and treatment is carried out based thereon (see Non-Patent Document 2). However, for the diagnosis of head-and-neck tumor, the imaging tests cannot qualitatively diagnose the tumor and in many instances make it difficult to differentiate the tumor from benign disease. The tissue diagnosis by biopsy, which is used as a definite diagnosis, also sometimes makes the determination of progression and invasion degrees of the tumor difficult as well as at present not enabling the prediction of prognosis thereof even when the basic hematoxylin-eosin (HE) stain is used in combination with various immunostainings. Although several factors for prediction of onset and prognosis of the tumor are reported (Patent Documents 1 to 3), there currently exists no biomarker sufficient in both sensitivity and specificity.
Treatment of head-and-neck tumor is determined depending primarily on the disease stage and histopathological manifestation thereof; while radical single-stage extirpation is carried out for benign tumor, surgery, radiotherapy and chemotherapy are used for malignant tumor and the combination thereof is required to be performed for advanced cancer. Surgery for head-and-neck tumor prominently damages the head-and-neck and the face surface cosmetically as well as highly affecting physical functions such as phonation and deglutition and therefore is highly invasive physically and psychologically, so that it causes a substantial reduction in QOL (quality of life). Even the combination of these treatments also makes the 5-year survival rate remain on the order of 30% for advanced cancer (see Non-Patent Document 2), and its therapeutic effect can never be said even now to be high. In addition, there are observed individual variations in therapeutic effect and prognosis, which are probably due to mutated gene and its abnormal expression level in tumor tissue (see Non-Patent Documents 3 and 4); however, to date the diagnosis of head-and-neck tumor at the gene level has not been carried out.
As described above, an increase in head-and-neck tumor is predicted in Japan, which is reaching an aging society; however, for prediction of onset thereof, to date no useful biomarker has been found (see Patent Documents 4 and 5 and Non-Patent Document 6) although an association of the onset with smoking, drinking, backflow of stomach acid, or overuse of voice is epidemiologically suggested (Non-Patent Document 5).
Meanwhile, a microRNA is a single-stranded RNA which is present in cells, not translated into protein, and on the order of 22 bases long (see Non-Patent Document 7). It was discovered in C. elegans in 1993 and thereafter also in a vertebrate in 2001 and is conserved beyond species. Currently, about 1,000 microRNAs are predicted to be present on the human genome; 700 or more of microRNAs have so far been cloned. MicroRNAs are believed to control genes in 30% of protein-coding regions on the genome (see Non-Patent Document 8); therefore, the functional failure of microRNAs has a possibility of causing various diseases. However, to date a very few microRNAs have biological roles elucidated; future analysis is awaited. Reports of microRNAs for head-and-neck tumor are found here and there in the case of using tumor cell lines (see Non-Patent Documents 9 and 10); however, up to date no report in which a patient's clinical specimen is used is found.